No one in the world understands quantum mechanics – this is the main thing you need to know about it. Yes, many physicists have learned to use its laws and even to predict phenomena by quantum calculations. But it is still not clear why the presence of an observer determines the fate of the system and forces it to make a choice in favor of one state. “Theories and practices” picked up examples of experiments, the outcome of which is inevitably influenced by the observer, and tried to figure out what quantum mechanics is going to do with such interference of consciousness in material reality.
Shroedinger `s cat
Today, there are many interpretations of quantum mechanics, the most popular among which is Copenhagen. Its main provisions in the 1920s were formulated by Niels Bohr and Werner Heisenberg. And the central term of the Copenhagen interpretation was the wave function – a mathematical function that contains information about all possible states of a quantum system in which it simultaneously resides.
According to the Copenhagen interpretation, it is possible to determine the state of the system for certain, only observation can distinguish it from the others (the wave function only helps to calculate mathematically the probability of finding the system in one state or another). It can be said that after observation the quantum system becomes classical: it instantly ceases to coexist in many states at once in favor of one of them.
This approach has always had opponents (remember, at least, “God does not play dice” by Albert Einstein), but the accuracy of calculations and predictions took its toll. However, recently supporters of the Copenhagen interpretation are becoming less and less and not the last reason for this – the very mysterious instantaneous collapse of the wave function during measurement. The famous thought experiment of Erwin Schrödinger with the poor fellow, the cat was called to show the absurdity of this phenomenon.
So, we remind the content of the experiment. A live cat, an ampoule with poison and some mechanism that can put the poison into action at random is placed in a black box. For example, one radioactive atom, the decay of which breaks the ampoule. The exact time of the decay of the atom is unknown. Only half-life is known: the time during which decay will occur with a probability of 50%.
It turns out that for an external observer the cat inside the box exists in two states at once: it is either alive if everything goes well, or dead, if the disintegration has occurred and the ampule has broken. Both of these states are described by the cat’s wave function, which changes over time: the farther away, the more likely that radioactive decay has already happened. But as soon as the box opens, the wave function collapses and we immediately see the outcome of the slaughter experiment.
It turns out that until the observer opens the box, the cat will forever balance on the border between life and death, and only the observer’s action will determine its fate. This is the absurdity pointed to by Schrödinger.
According to a survey of the largest physicists conducted by The New York Times newspaper, the experience with electron diffraction, delivered in 1961 by Klaus Jenson, became one of the most beautiful in the history of science. What is its essence?
There is a source radiating a stream of electrons in the direction of the screen-photographic plate. And there is a barrier in the path of these electrons – a copper plate with two slits. What kind of picture on the screen can you expect if you present electrons just as small charged balls? Two illuminated bands opposite the cracks.
In fact, a much more complex pattern of alternating black and white stripes appears on the screen. The fact is that when passing through the slits, electrons begin to behave not as particles, but as waves (just as photons, particles of light can be waves at the same time). Then these waves interact in space, weakening somewhere and strengthening each other, and as a result a complex picture of alternating light and dark stripes appears on the screen.
At the same time, the result of the experiment does not change, and if the electrons are allowed to flow through the slit not in a continuous flow, but singly, even one particle can be a wave at the same time. Even one electron can simultaneously pass through two slots (and this is another important provision of the Copenhagen interpretation of quantum mechanics – objects can simultaneously exhibit their “usual” material properties and exotic wave properties).
But what is the observer? With that already complicated story with him it became even more difficult. When in such experiments, physicists tried to fix with the help of instruments, through which gap the electron actually passed, the picture on the screen changed dramatically and became “classic”: two illuminated areas opposite the gaps and no alternating bands.
The electrons did not seem to want to manifest their wave nature under the watchful eye of the observer. Adjusted for his instinctive desire to see a simple and clear picture. Mystic? There is a much simpler explanation: no observation of the system can be carried out without physically affecting it. But let’s come back to this a little later.
Experiments on the diffraction of particles were put not only on electrons, but also on where large objects. For example, fullerenes are large, closed molecules composed of dozens of carbon atoms (for example, a fullerene of sixty carbon atoms is very similar in shape to a soccer ball: a hollow sphere made of five or hexagons).
Recently, a group from the University of Vienna led by Professor Zeilinger attempted to introduce an element of observation into such experiments. To do this, they irradiated the moving fullerene molecules with a laser beam. Then, heated by an external effect, the molecules began to glow and, inevitably, found their place in space for the observer.
Together with this innovation, the behavior of molecules has changed. Prior to the start of total surveillance, fullerenes quite successfully skirted obstacles (showed wave properties), like electrons from the previous example, passing through an opaque screen. But later, with the advent of the observer, the fullerenes calmed down and began to behave like quite law-abiding particles of matter.
One of the most famous laws of the quantum world is the Heisenberg uncertainty principle: it is impossible to simultaneously determine the position and velocity of a quantum object. The more accurately we measure the momentum of a particle, the less accurately we can measure its position. But the action of quantum laws operating at the level of tiny particles is usually imperceptible in our world of large macro-objects.
Therefore, the more recent experiments by the group of Professor Schwab from the United States, in which quantum effects were shown not at the level of the same electrons or fullerene molecules (their characteristic diameter is about 1 nm), but on a slightly more tangible object – a tiny aluminum strip.
This strip was fixed on both sides so that its middle was suspended and could vibrate under external influence. In addition, next to the strip was a device capable of accurately recording its position.
As a result, experimenters discovered two interesting effects. Firstly, any measurement of the position of the object, the observation of the strip did not pass without a trace for it – after each measurement the position of the strip changed. Roughly speaking, the experimenters with great precision determined the coordinates of the strip and thus, according to the Heisenberg principle, changed its speed, and hence the subsequent position.
Secondly, which is quite unexpected, some measurements also led to the cooling of the strip. It turns out that the observer can only change the physical characteristics of the objects with his presence. It sounds absolutely unbelievable, but to the credit of physicists, we say that they were not taken aback – now the group of Professor Schwab is thinking how to use the detected effect to cool electronic microcircuits.
As it is known, unstable radioactive particles disintegrate in the world not only for the sake of experiments on cats, but also completely by themselves. In addition, each particle is characterized by an average lifetime, which, it turns out, can increase under the watchful eye of the observer.
This quantum effect was predicted for the first time in the 1960s, and its brilliant experimental confirmation appeared in an article published in 2006 by the group of Nobel laureate in physics Wolfgang Ketterle from the Massachusetts Institute of Technology.
In this paper, we studied the decay of unstable excited rubidium atoms (they decay into rubidium atoms in the ground state and photons). Immediately after the preparation of the system, the excitations of the atoms behind them began to be observed — they were illuminated by a laser beam. In this case, the observation was conducted in two modes: continuous (small light pulses are constantly fed into the system) and pulsed (the system is occasionally irradiated with more powerful pulses).
The results obtained perfectly matched the theoretical predictions. External light effects really slow down the decay of particles, as if returning them to their original, far from decay state. At the same time, the magnitude of the effect for the two studied modes also coincides with the predictions. And maximally the life of unstable excited rubidium atoms could be extended 30 times.
Electrons and fullerenes cease to show their wave properties, aluminum plates are cooled, and unstable particles freeze in their decay: the world is changing under the all-powerful eye of the observer. What is not evidence of the involvement of our mind in the work of the world around? So maybe Carl Jung and Wolfgang Pauli (Austrian physicist, Nobel Prize winner, one of the pioneers of quantum mechanics) were right when they said that the laws of physics and consciousness should be considered as complementary?
But so there is only one step to the on-call recognition: the whole world around is the illusory creation of our mind. Scary? (“Do you really think that the Moon exists only when you look at it?” Einstein commented on the principles of quantum mechanics). Then we will try again to turn to physicists. Moreover, in recent years they have less favored the Copenhagen interpretation of quantum mechanics with its mysterious collapse wave function, which is replaced by another, quite mundane and reliable term – decoherence.
The point is this – in all the described experiments with observation, experimenters inevitably influenced the system. Lighted it with a laser, installed measuring devices. And this is a common, very important principle: you can not observe the system, measure its properties without interacting with it. And where the interaction is, there is a change in properties. Especially, when the tiny bits of quantum objects interact with a tiny quantum system. So the eternal, Buddhist neutrality of the observer is impossible.
This is precisely what explains the term “decoherence” – a process that is irreversible from the point of view of thermodynamics, a violation of the quantum properties of a system when it interacts with another, large system. During such an interaction, the quantum system loses its original features and becomes classical, “obeys” the large system. This explains the paradox with Schrödinger’s cat: a cat is such a large system that it simply cannot be isolated from the world. The very formulation of a mental experiment is not entirely correct.
In any case, compared with reality as an act of creation of consciousness, decoherence sounds much more relaxed. Even maybe too calm. After all, with this approach, the entire classical world becomes one big decoherence effect. And according to the authors of one of the most serious books in this area, statements like “there are no particles in the world” or “there is no time at a fundamental level” also logically follow from such approaches.
A creative observer or all-powerful decoherence? We have to choose from two evils. But remember – now scientists are becoming more and more convinced that the basis of our thought processes are those very notorious quantum effects. So where the observation ends and the reality begins – each of us has to choose.